1. Field of the Invention
The present invention relates to a processing apparatus including a reaction vessel to subject a substrate to a film forming process using a film forming gas in a vacuum therein, and a drive shaft extending through a hole formed in a wall of the reaction vessel, and a processing method to be carried out by the same processing apparatus.
2. Description of the Related Art
There are known vertical heat-treatment apparatus for heat-treating semiconductor wafers (hereinafter referred to simply as "wafers") in a batch processing system. Heat-treatment processes include a film forming processes called low-pressure CVD (hereinafter referred to as "LPCVD") processes, oxidation processes, impurity diffusion processes. Processing systems respectively for carrying out LPCVD processes, oxidation processes and impurity diffusion processes differ somewhat in construction from each other because furnaces for LPCVD processes, and those for oxidation processes and impurity diffusion processes differ from each other in process temperature, process pressure and gas supplying method. In all those systems, a wafer boat holding wafers in layers and mounted on a lid is carried usually from below into a vertical reaction vessel through an opening formed in the bottom wall of the reaction vessel, and the opening is closed by the lid supporting the wafer boat.
In some processing systems of such a type, the wafer boat is rotated about a vertical axis to subject the entire surfaces of the wafers uniformly to heat treatment, In such processing systems the wafer boat is supported on a rotation shaft extending through the lid. A mechanism for inserting the rotation shaft through the lid into the reaction vessel of a LPCVD system will be described, by way of example, with reference to FIG. 3.
Referring to FIG. 3, a reaction vessel comprises a double-wall reaction tube 10 and a manifold 11 connected to a lower part of the reaction tube 10. An opening formed at the lower end of the manifold 11 is closed by a lid 12. A rotation shaft 13 is extended through a tubular member 14 of a metal. A turntable 15 is attached to an upper end part of the rotation shaft 13, and a driven pulley 16 to be driven by a motor, not shown, is attached to a lower end part of the rotation shaft 13. A bearing unit 17 for supporting the rotation shaft 13 is contained in the tubular member 14. Also contained in the tubular member 14 is a magnetic sealing unit 18 for hermetically sealing the reaction vessel. The magnetic sealing unit 18 is disposed above the bearing unit 17.
When the interior of th(e reaction vessel is evacuated to a high vacuum on the order of 10.sup.-7 torr, particles emanated from a rotary mechanism including the rotation shaft 13 and the bearing unit 17, and vapors of a magnetic fluid leak into the evacuated reaction vessel. Circuit patterns of semiconductor devices have been progressively miniaturized and the severity of limits to the contamination of wafers has grown accordingly. Particles must be avoided on wafers since they cause deleterious effects leading to device degradation. Furthermore, if the film forming gas leaks into the rotary mechanism, the film forming gas comes into contact with cold parts and produces reaction byproducts. It is possible that such byproducts mix with the magnetic fluid to increase resistance against the rotating operation of the rotary mechanism.
The inventors of the present invention have made studies to provide a reaction vessel capable of being used for CVD, oxidation and diffusion through the enhancement of the corrosion resistance of the manifold 11. If a reaction vessel is used for wet oxidation, moisture will leak into the rotary mechanism, and the moisture will be diffused into the reaction vessel when the reaction vessel is used for forming an insulating film by LPCVD and will deteriorate the insulating capability of the insulating film. If hydrogen chloride gas leaks into the rotary mechanism during an oxidation process, the metal components of the rotary mechanism will be corroded, the magnetic fluid of the magnetic seal will be deteriorated and the sealing function of the magnetic seal will be deteriorated. Particularly, in a state where moisture condenses on the components of the rotary mechanism, the components of the rotary mechanism are subject to rapid corrosion and deterioration.